FATTY-ACID ESTERIFICATION DURING DIFFERENTIATION OF THE HUMAN INTESTINAL-CELL LINE CACO-2

The Caco-2 human intestinal cell line was used to examine fatty acid e sterification during development of the enterocytic phenotype. Acyl-Co A synthetase activity increased approximately 40%, and the incorporati on of palmitic acid into triacylglycerol relative to phosphatidylcholi ne increased nearly 2-fold during Caco-2 differentiation. A rate-limit ing enzyme activity in the glycerol 3-phosphate pathway of triacylglyc erol synthesis, glycerol-3-phosphate acyltransferase, was at levels co mparable with rat jejunum and remained unchanged during differentiatio n. In contrast, the activity of monoacylglycerol acyltransferase, whic h is unique to the monoacylglycerol pathway of triacylglycerol synthes is, was present at <7% of the levels in rat jejunum. Further analysis of the glycerol 3-phosphate pathway showed that the rate-limiting enzy me activities for diacylglycerol conversion to triacylglycerol, diacyl glycerol acyltransferase, and phosphatidylcholine, CTP:phosphocholine cytidylyltransferase, increased 2-3-fold and decreased approximately 4 0%, respectively, during Caco-2 differentiation. In addition, a 2-fold increase in cellular diacylglycerol mass was observed during enterocy tic conversion. These data indicate that fatty acid esterification to triacylglycerol in Caco-2 cells occurs primarily via the glycerol 3-ph osphate pathway. Furthermore, the differentiation-dependent increase i n fatty acid esterification to triacylglycerol relative to phosphatidy lcholine appears to result from increased utilization of diacylglycero l to synthesize triacylglycerol and a concomitant decrease in diacylgl ycerol utilization for phosphatidylcholine synthesis.